Fish Oil and Cod Liver Oil (EPA & DHA)

Most fish oil supplements are 18% EPA and 12% DHA, or a total of 30% omega-3. These omega-3 fatty acids, unlike the omega-3 fatty acid found in flaxseed oil and other vegetable oils (such as alpha linolenic acid), keep blood triglycerides in check (high triglycerides are generally linked with increased risk of heart disease) and may inhibit the progression of atherosclerosis.1 EPA and DHA keep blood from clotting too quickly.

EPA and DHA also have anti-inflammatory activity. As a result, fish oil is used to help people with various inflammatory conditions, such as Crohn’s disease2 and rheumatoid arthritis.3 The anti-inflammatory effects of EPA and DHA may also account for the findings of some reports that show fish oil supplementation helps some people with kidney diseases4 5 6 and may help protect against chronic obstructive pulmonary disease.7

The omega-3 fatty acids in fish oil help to balance the omega-6 fatty acids, which are found mostly in vegetable oils. When these two groups of fatty acids are out of balance, the body releases chemicals that promote inflammation. People appear to produce more of these inflammatory chemicals when experiencing psychological stress (e.g., academic examinations). With a fatty acid imbalance, inflammatory response to stress appears to be amplified.8

Prostaglandins are hormone-like substances produced within the body that regulate dilation of blood vessels, inflammatory response, and other critical processes. Omega-3 fatty acids are needed for prostaglandin formation. Probably as a result of their effect on prostaglandins responsible for blood vessel dilation, a double-blind trial found that omega-3 fatty acids from fish oil helped to treat people with Raynaud’s disease.9

Schizophrenia is linked with abnormalities in fatty acid metabolism, and preliminary research suggests that fish oil supplementation may be helpful to people with schizophrenia.10 However, a double-blind study that used 3 grams per day of eicosapentaenoic acid failed to demonstrate any benefit for patients with chronic schizophrenia.11

DHA is essential for vision in infants. Researchers are now studying this relationship to better understand how much DHA is needed.

EPA and DHA also modulate immune function,12 probably as a result of their effect on prostaglandin production. Perhaps as a result of this effect, fish oil has helped prevent some types of cancer in animals13 14 15 and humans,16 although this evidence remains preliminary.

Preliminary evidence also shows that omega-3 fatty acids from fish oil may help regulate the rhythm of the heart. EPA and DHA have been reported to help prevent cardiac arrhythmias.17

Where is fish oil and cod liver oil (epa - dha) found?EPA and DHA are found in mackerel, salmon, herring, sardines, sablefish (black cod), anchovies, albacore tuna, and wild game. Cod liver oil contains large amounts of EPA and DHA. Fish oil supplements typically contain 18% EPA and 12% DHA, though more purified (i.e., higher in EPA and DHA) fish oil supplements are sometimes available. In addition, DHA is available in a supplement that does not contain significant amounts of EPA.

Fish oil has been used in connection with the following conditions(refer to the individual health concern for complete information):

For an herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support and/or minimal health benefit.

Who is likely to be deficient of fish oil and cod liver oil (epa - dha)?So-called “primitive” diets have much higher levels of EPA and DHA than modern diets. As a result, some researchers and doctors believe that most people who eat a typical western diet are likely to be consuming less-than-optimal amounts of EPA and DHA. To a very limited extent, omega-3 fatty acids from vegetable sources, such as flaxseed oil, can convert to EPA.

At least four studies have reported a reduced blood level of omega-3 fatty acids in people with depression.18 19 20 21

People with rheumatoid arthritis have been found to have decreased levels of omega-3 fatty acids, such as are found in fish oil, in their joint fluid and blood.22

How much fish oil and cod liver oil (epa - dha) is usually taken?Presumably, healthy people who frequently eat fatty fish (several times per week) have no need to supplement with fish oil. How much EPA and DHA, if any, should be supplemented by healthy people who do not eat much fatty fish, remains unclear.

Most researchers studying the effects of EPA and DHA in humans who have a variety of health conditions have given those people at least 3 grams of the total of EPA plus DHA—an amount that may require 10 grams of fish oil, because most fish oil contains only 18% EPA and 12% DHA.

The health benefits for people with Crohn’s disease have been reported with a special, enteric-coated preparation of purified EPA/DHA manufactured from fish oil. This preparation of purified fatty acids has also been reported to not cause the gastrointestinal symptoms that often result from taking regular fish oil supplements, again suggesting unique benefit.23

In one trial, the maximum amount of fish oil tolerated by people being treated for cancer-related weight loss was reported to be approximately 21 grams per day.24 However, in people who do not have cancer, the maximum tolerated amount may be different.

Are there any side effects or interactions with fish oil and cod liver oil (epa - dha)?While those with heart disease and diabetes have often been reported to benefit from supplementation with fish oil,25 26 both groups should check with their doctor before taking more than 3 grams of fish oil per day for several months. Elevations in blood sugar and cholesterol levels may occur in some people who take fish oil.27

The increase in blood sugar appears to be related in part to the amount of fish oil used.28 Some evidence suggests that adding vitamin E to fish oil may prevent the fish oil-induced increase in blood sugar levels.29 In other research, the impairment of sugar metabolism sometimes caused by supplementation with fish oil has been prevented by the addition of half an hour of moderate exercise three times a week.30

While supplementation with fish oil consistently lowers triglycerides, the effect of fish oil on LDL (“bad”) cholesterol varies, and in some people, fish oil supplementation has been reported to increase LDL levels.31 People who took fish oil and who also took 15 grams of pectin per day were reported to have reductions in LDL cholesterol.32 This suggests that pectin may overcome the occasional problem of increased LDL cholesterol reported in people who supplement with fish oil. The LDL-cholesterol raising effect of EPA and DHA has also been reported to be prevented by taking garlic supplements (or presumably including garlic in the diet) along with EPA and DHA.33

Are there any drug interactions?Certain medicines may interact with Fish Oil and Cod Liver Oil. Refer to drug interactions for a list of those medicines